In vehicle air-conditioning systems used in electrically driven vehicles such as EV vehicles, HEV vehicles, and PHEV vehicles, heating operation utilizing combustion waste heat of engine cooling water (coolant) or the like cannot be performed. Therefore, a heat-pump-type air-conditioning system using an electric compressor is expected. However, in a case where a reverse type heat pump is used, heat exchangers such as pipes, an evaporator, and a condenser configuring a refrigerant circuit have to be usable together under different temperature and pressure conditions of cooling operation and heating operation, a vehicle air-conditioning system (hereinafter, referred to as a current system) applied to a current engine-driven vehicle has to be totally changed.
A heat-pump-type vehicle air-conditioning system, in which a heating refrigerant circuit is configured by utilizing a cooling refrigerant circuit of the current system as it is, and adding a vehicle interior condenser (also referred to as sub condenser) provided in an HVAC unit (Heating Ventilation and Air Conditioning Unit), or a vehicle exterior evaporator to the circuit through a selector valve, a bypass circuit, and the like, is provided by, for example, Patent Citation 1.
On the other hand, Patent Citation 2 discloses a heat-pump-type vehicle air-conditioning system, in which a heating bypass circuit is connected to a vehicle exterior condenser through a four-way valve, and a sub condenser is connected to an upstream side of an expansion valve, and the sub condenser is disposed on a downstream side of an evaporator in an HVAC unit. Patent Citation 3 discloses a heat-pump-type vehicle air-conditioning system, in which an evaporator is disposed on an upstream side in an HVAC unit, a vehicle interior condenser is disposed on a downstream side, a vehicle exterior heat exchanger which functions as a condenser during cooling and functions as an evaporator during heating is connected to a refrigerant inlet side of the vehicle interior condenser through a selector valve, a bypass circuit, and the like.
Furthermore, Patent Citation 4 discloses a heat-pump-type vehicle air-conditioning system, in which a vehicle interior evaporator is provided on an upstream side inside an HVAC, a heater core in which heat medium such as hot coolant can be circulated is provided on a downstream side, a refrigerant/heat medium heat exchanger that heats the heat medium such as hot coolant circulated in the heater core is provided in a discharge pipe of an electric compressor, and a heat pump cycle is configured by the refrigerant/heat medium heat exchanger, the vehicle exterior heat exchanger, the vehicle interior evaporator, and the like.
Patent Citation 1: Japanese Unexamined Patent Application, Publication No. 2012-96634
Patent Citation 2: Japanese Unexamined Patent Application, Publication No. Hei 11-170849
Patent Citation 3: Japanese Unexamined Patent Application, Publication No. Hei 5-319077 (the Publication of Japanese Patent No. 3538845)
Patent Citation 4: Japanese Unexamined Patent Application, Publication No. Hei 9-286225 (the Publication of Japanese Patent No. 3704814)